A polymer composition of this general type is known from U.K. Patent specifications Nos. 991,422 and 1,253,266 and from the U.S. Pat. Nos. 3,988,389 and 3,954,905.
The U.K. Patent Specification No. 991,422 describes mixtures of a polycarbonate and a polymer obtained by graft polymerizing a vinyl aromatic compound and an unsaturated nitrile compound in the presence of polybutadiene. According to U.K. Patent No. 1,253,266, the heat resistance, notch impact strength, and hardness of such mixtures can be improved by incorporating therein a copolymer that contains at least 50 weight % of .alpha.-methylstyrene.
U.S. Pat. No. 3,988,389 discloses that the strength of fusion welds of mixtures formulated according to these patents can be improved by using a graft copolymer having 40-80 weight % of rubber and a mean particle size between 0.2 and 5 .mu.m. U.S. Pat. No. 3,954,905 discloses that such improvement can also be achieved by using a graft copolymer having a mean particle size between 0.05 and 0.19 .mu.m.
European Patent Application No. 5202 describes a polymer composition based on a polycarbonate, a first ABS graft copolymer having a rubber content of 5-50 weight %, a second ABS graft copolymer having a rubber content of 60-90 weight %, and, optionally, a copolymer. The object thereof is to provide compositions which retain their impact resistance at very low temperatures.